Fish
Fish Gestation Period: Calculator and Chart for Mollies, Guppies, Platies and More
Livebearing aquarium fish are pregnant for 28 days on average. The normal range is 20 to 40 days, and each species has its own range. Egg-laying fish such as bettas and goldfish do not carry their young: the eggs hatch 2 to 7 days after laying. Pick your fish in the calculator below, enter the date and receive the expected birth or hatch date.
28 days
Livebearer average
20–40
Molly range (days)
2–7
Egg-layer hatch (days)
What Is the Fish Gestation Calculator?
The fish gestation calculator converts a date into an expected birth or hatch date for 8 aquarium fish. For a livebearer (molly, guppy, platy or swordtail) you enter the date the fish mated, and the calculator adds the gestation length. For an egg-layer (betta, goldfish, angelfish or zebra danio) you enter the date the eggs were laid, and the calculator adds the hatch time.
The calculator returns:
- Expected date of birth or hatching The most likely date, counted from your start date.
- Earliest and latest dates Based on the normal range for the species.
- Calendar file Add the dates to Google Calendar, Apple Calendar and Outlook.
Example: a molly that mated on 1 March 2026 is due on 29 March 2026 (day 28). The range for a molly runs from 21 March 2026 (day 20) to 10 April 2026 (day 40).
Problems the Fish Gestation Calculator Solves
- You do not know when the fry are due. The calculator applies the species length to the mating date, so you know the day your fish enters its birth window.
- The range is wide. A molly gives birth anywhere from day 20 to day 40, a spread of 20 days. The calculator shows the earliest date, the average date and the latest date.
- You keep several species. Mollies, guppies, platies and swordtails each carry young for a different range. The calculator holds a separate length for each.
- You breed egg-layers. A betta, angelfish or zebra danio egg hatches in 2 to 4 days, and a goldfish egg in 4 to 7 days. The calculator dates the hatch from the day the eggs were laid.
How the Fish Gestation Calculator Works
- Select the fish. Choose a molly, guppy, platy, swordtail, betta, goldfish, angelfish or zebra danio.
- Enter the date. Use the date the fish mated (livebearers) or the date the eggs were laid (egg-layers).
- Read the result. See the expected date and the range for your fish.
- Save or share it. Add the dates to your calendar or copy a link that reopens the calculator with your dates.
Fish Gestation and Hatching Times
This chart lists the average and the range for each fish in the calculator, and how many young or eggs one birth or spawning produces.
| Fish | Type | Average days | Range (days) | Young or eggs |
|---|---|---|---|---|
| Molly | Livebearer | 28 | 20–40 | 20–60 fry |
| Guppy | Livebearer | 28 | 21–30 | 20–50 fry |
| Platy | Livebearer | 28 | 24–30 | 20–40 fry |
| Swordtail | Livebearer | 28 | 24–30 | 20–80 fry |
| Betta | Egg-layer | 3 | 2–3 | 30–500 eggs |
| Goldfish | Egg-layer | 5 | 4–7 | hundreds of eggs |
| Angelfish | Egg-layer | 3 | 2–3 | 100–500 eggs |
| Zebra danio | Egg-layer | 3 | 2–4 | 100–200 eggs |
Source: published averages, loaded into the calculator. Each fish falls anywhere inside its range.
How Long Livebearers Carry Their Young
Livebearers carry developing young inside the body and give birth to free-swimming fry. The calculator holds four species:
- Molly: 28 days on average (20–40), with 20–60 fry per birth.
- Guppy: 28 days on average (21–30), with 20–50 fry per birth.
- Platy: 28 days on average (24–30), with 20–40 fry per birth.
- Swordtail: 28 days on average (24–30), with 20–80 fry per birth.
How Long Egg-Layers Take to Hatch
Egg-laying fish release eggs, and the eggs hatch after a short time:
- Betta: 3 days on average (2–3), with 30–500 eggs per spawning.
- Goldfish: 5 days on average (4–7), with hundreds of eggs per spawning.
- Angelfish: 3 days on average (2–3), with 100–500 eggs per spawning.
- Zebra danio: 3 days on average (2–4), with 100–200 eggs per spawning.
Why Choose Animal Gestation Calculator for Your Fish
- A range with every date. You see the earliest, average and latest date, not one guess.
- Eight fish in one calculator. Livebearers and egg-layers use the correct start date for each.
- Calendar export. Add the dates to Google Calendar, Apple Calendar or Outlook.
- Free and private. No account is required, and your entries stay in your browser.
- Published sources. Every figure comes from a published average, and every page labels it an estimate.
Who Uses the Fish Gestation Calculator
- Aquarium keepers with a pregnant molly, guppy, platy or swordtail.
- Fish breeders tracking mating and spawning dates.
- Fish-store staff planning tank space for fry.
- Biology students comparing livebearers and egg-layers.
Gestation Calculators for Other Animals
Compare these figures with the dog gestation calculator (63 days), the cat gestation calculator (64 days), the rabbit gestation calculator (31 days), the hamster gestation calculator (16 days) and the guinea pig gestation calculator (68 days). For egg-laying animals on land, use the bird incubation calculator. The home page lists the gestation period of all 75 animals.
Frequently Asked Questions
How long are mollies pregnant?
A molly is pregnant for 28 days on average. The normal range is 20 to 40 days, and a birth produces 20–60 fry fry. Use the fish calculator with the date your molly mated.
How long is a guppy pregnant?
A guppy is pregnant for 28 days on average, with a normal range of 21–30 days. A birth produces 20–50 fry fry.
How long is a platy pregnant?
A platy is pregnant for 28 days on average, with a normal range of 24–30 days. A birth produces 20–40 fry fry.
How long is a swordtail pregnant?
A swordtail is pregnant for 28 days on average, with a normal range of 24–30 days. A birth produces 20–80 fry fry.
Do all fish get pregnant?
No. Livebearers such as mollies, guppies, platies and swordtails carry their young and give birth to fry. Egg-laying fish such as bettas, goldfish, angelfish and zebra danios lay eggs that hatch 2 to 7 days later.
How long do betta eggs take to hatch?
Betta eggs hatch after 3 days on average, within a range of 2–3 days. One spawning produces 30–500 eggs eggs.
How long do goldfish eggs take to hatch?
Goldfish eggs hatch after 5 days on average, within a range of 4–7 days.
How do I calculate a fish's due date?
Add the average gestation length to the mating date. A molly that mated on 1 March 2026 is due on 29 March 2026, within a range from 21 March to 10 April. The calculator does the arithmetic for any fish and date.
Why is the range so wide for mollies?
The published range for a molly is 20 to 40 days, a spread of 20 days, so the calculator shows an earliest date, an average date and a latest date.
How accurate is the calculator?
The calculator gives an estimate from the published average. Each fish falls anywhere inside the range for its species.
Is the calculator veterinary advice?
No. The calculator provides estimates for planning only. Every animal is different. Consult a qualified veterinarian or aquatic specialist about your fish.
Find Your Due Date Now
Pick your fish, enter the date and receive the birth or hatch date and range in seconds.
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Important notice: All dates and figures are estimates for planning only and are not veterinary advice. Consult a qualified veterinarian.